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Sun, 26 Jul 2026 06:59:02 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id BGGKDzawZWosewAAD6G6ig (envelope-from ); Sun, 26 Jul 2026 06:59:02 +0000 Date: Sun, 26 Jul 2026 08:59:01 +0200 Message-ID: <87cxwab5je.wl-tiwai@suse.de> From: Takashi Iwai To: Baul Lee Cc: linux-sound@vger.kernel.org, perex@perex.cz, tiwai@suse.com, federico.kirschbaum@xbow.com, stable@vger.kernel.org Subject: Re: [PATCH] ALSA: usb-audio: fix use-after-free in ump_to_endpoint() In-Reply-To: <20260726051337.41124-1-baul.lee@xbow.com> References: <20260726051337.41124-1-baul.lee@xbow.com> User-Agent: Wanderlust/2.15.9 (Almost Unreal) Emacs/30.2 Mule/6.0 Precedence: bulk X-Mailing-List: linux-sound@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 (generated by SEMI-EPG 1.14.7 - "Harue") Content-Type: text/plain; charset=US-ASCII X-Spam-Score: -3.30 X-Spam-Level: X-Spam-Flag: NO X-Spamd-Result: default: False [-3.30 / 50.00]; BAYES_HAM(-3.00)[100.00%]; MID_CONTAINS_FROM(1.00)[]; NEURAL_HAM_LONG(-1.00)[-1.000]; NEURAL_HAM_SHORT(-0.20)[-1.000]; MIME_GOOD(-0.10)[text/plain]; RCVD_VIA_SMTP_AUTH(0.00)[]; ARC_NA(0.00)[]; RCVD_TLS_ALL(0.00)[]; TO_DN_SOME(0.00)[]; MIME_TRACE(0.00)[0:+]; FUZZY_RATELIMITED(0.00)[rspamd.com]; DKIM_SIGNED(0.00)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; TO_MATCH_ENVRCPT_ALL(0.00)[]; FROM_HAS_DN(0.00)[]; RCPT_COUNT_FIVE(0.00)[6]; FROM_EQ_ENVFROM(0.00)[]; RCVD_COUNT_TWO(0.00)[2]; DBL_BLOCKED_OPENRESOLVER(0.00)[suse.de:mid,imap1.dmz-prg2.suse.org:helo,xbow.com:email] On Sun, 26 Jul 2026 07:13:37 +0200, Baul Lee wrote: > > create_midi2_ump() registers a card-owned snd_ump_endpoint and stores a > back-pointer to its per-interface snd_usb_midi2_ump object in > ump->private_data, but it never installs an ump->private_free hook and > never clears that pointer. > > If a later step of snd_usb_midi_v2_create() fails, its error path calls > free_all_midi2_umps(), which kfree()s the snd_usb_midi2_ump object while > the already-registered endpoint keeps pointing at it. The created > /dev/snd/umpC*D* node stays exposed, so the first operation of any UMP > open, ump_to_endpoint(), dereferences the dangling ump->private_data and > reads rmidi->eps[dir] out of freed memory. > > A malicious USB MIDI 2.0 device that makes creation fail after the > endpoint is registered can thus trigger a slab use-after-free read on a > subsequent open of the UMP node. > > Clear the endpoint's back-pointer before freeing the object, and let > ump_to_endpoint() tolerate a NULL private_data so the open/close/trigger > callbacks fail cleanly (their callers already handle a NULL endpoint) > instead of dereferencing a stale pointer. > > Discovered by XBOW, triaged by Baul Lee > > Fixes: ff49d1df79ae ("ALSA: usb-audio: USB MIDI 2.0 UMP support") > Reported-by: Federico Kirschbaum > Reported-by: Baul Lee > Cc: stable@vger.kernel.org > Signed-off-by: Baul Lee Applied now. Thanks. Takashi